Recently various HIV-1 infectable humanized mouse models (BLT, hNSG) have been advanced which show great promise for vaccine development. In this proposal, we will develop a new humanized mouse model for testing HIV-1 vaccines containing a-gal epitopes. Our previous work demonstrated that immunogenicity of HIV-1 gp120 protein engineered to express a-gal epitopes was 100-fold higher than that lacking the a-gal epitope in the a-1, 3-galactosyltransferase knockout (KO) mice which express anti-Gal antibodies. The enhancement is likely due to an increased uptake of vaccine antigen plus anti-Gal antibody complexes by antigen presenting cells. Unlike humans, the tissues in all existing humanized mouse models express a-gal epitopes, and lack B cells secreting anti-Gal antibodies. The new proposed humanized mouse model will be the first humanized non-primate animal model with tissues lacking a-gal epitopes and B cells secreting anti-Gal antibodies, as in humans. Specifically, we aim to: 1) construct the new mouse model by breeding the a1,3 GT knockout (KO) mice which lack a-gal epitopes and produce anti-Gal antibodies, with NSG mice (NOD/SCID IL2r gamma (null) and 2) the new mouse strain (referred as NSG/a-galnull) will be engrafted with human fetal tissues and CD34+ stem cells to develop a mature human immune system. 3) After engraftment, these new humanized mice will be used to test the efficacy of an HIV-1 gp140 trimer vaccine containing a-gal epitopes. We will assess induction of humoral and cellular immune responses to the vaccine as well protection from HIV-1 infection. Success of these studies will provide justification for testing a-gal expressing vaccines in monkeys which, like humans produce anti-gal antibodies and expedite pre-clinical development of HIV-1 vaccine candidates and human clinical trials. PUBLIC HEALTH RELEVANCE: More than 40 million people are currently infected with HIV worldwide and a vaccine is urgently needed. We propose to generate a new mouse model that can be used to test novel HIV vaccines.